Changes in atmospheric composition directly affect many aspects of life, determining climate, air quality and atmospheric inputs to ecosystems. In turn, these changes affect the fundamental necessities for human existence: human health, food production, ecosystem health and water. Atmospheric composition change research is therefore fundamental for the future orientation of Europe's Sustainable Development strategy. ACCENT, the European Network of Excellence on Atmospheric Composition Change, is funded by the European Commission under 6th Framework Programme in the area Global Change and Ecosystems. ACCENT’s goals are to promote a commonEuropean strategy for research on atmospheric composition change, to develop and maintain durable means of communication and collaboration within the European scientific community, to facilitate this research and to optimise two-way interaction with policy-makers and the general public. This volume collects the scientific contributions to the Second ACCENT Symposium which was held in Urbino from23 to 27 July 2007.Sandro Fuzzi, Coordinator of ACCENT, is Research Director at the Institute of Atmospheric Sciences and Climate of the Italian National Research Council (C.N.R.) and Head of the Research Group "Atmospheric Chemistry". He is also Coordinator of the Project "Global Change" of the Department Earth and Environment of the C.N.R. His main research interest is the physical and chemical processes of multiphase atmospheric systems (aerosols and clouds) and their effects on atmosphericcomposition change, climate, ecosystems and human health. Within these science themes, he has coordinated several national and international scientific projects and is/has been member of several international Committees and Panels: Commission on Atmospheric Chemistry and Global Pollution, Science Panel of the European Commission on Atmospheric Composition Change, Scientific Steering Committee of the EUREKA project EUROTRAC, International Commission on Clouds and Precipitation, Scientific Steering Committee of the International Global Atmospheric Chemistry Project (of which he has also been Co-Chair), European Strategy Forum on Research Infrastructures. He is author of over 100 papers in international peer-reviewed journals and of over 200 conference presentations, and has been Editor of 10 books/journal special issues. Michela Maione, Executive Secretary of ACCENT, is Associate Professor in Environmental Chemistry at the University of Urbino “Carlo Bo”, Faculty of Sciences and Technologies. Her main research interest is in the study of anthropogenic organic gases responsible for global change issues, like stratospheric ozone depletion and global warming. She has been involved in several national and international projects dealing with changes of the atmospheric gas phase composition.